This invention relates to electric lamps in general and, in particular, to a headlamp for motor vehicles designed to provide a lower beam pattern of clearcut outline.
A long familiar construction of vehicle headlamps was such that an electric bulb was disposed in from of a paraboloidal reflector, with the coiled filament of the bulb positioned approximately at the focus of the reflector and with the filament axis in alignment with the optical axis of the reflector. The front lens of the lamp was stepped to diverge the reflected beam, which was itself of circular cross section, generally horizontally, and to raise part of the reflected beam up to the horizon.
The lower beam pattern produced by this conventional method is unsatisfactory in the clarity of the delineation of its outline. The top edge cutoff of the beam pattern is particularly objectionable. Since the horizontally elongate lower beam pattern was produced by diverging the reflected beam of circular cross section, the top edgee cutoff of the resulting beam was not so well defined as could be desired. The light left unshaded above the top edge cutoff represents a source of glare which can to dazzle the drivers of other vehicles and so must be reduced to an absolute minimum.